This invention relates to improvements in a screw feed apparatus for use with a power screwdriving tool, and more particularly to an automatic screw feed apparatus in which a series of self-drilling screws carried in line at a regular space interval by a flexible, flat magazine belt are automatically supplied one after another to a forward end section of the screwdriving tool.
A conventional screwdriving tool as disclosed in U.S. Pat. No. 4,059,034 to Hornung has proposed a screw feed mechanism comprising a pair of feed wheels having sprocket teeth arranged to engage the notches of a flexible magazine belt carrying a series of self-drilling screws to be driven into a workpiece, and ratchet mechanism for rotating the feed wheels intermittently by one pitch in response to relative sliding motion between a slide member and a casing to feed the magazine belt for the purpose of automatically supplying the self-drilling screws one after another to the forward end section of the power tool. More particularly, this prior art screw feed mechanism includes a disc which causes oneway rotation of the pair of feed wheels which are in engagement with the screw carrier belt, said disc having a pin projecting at one side thereof so as to be engaged in a guide slot of the casing which is partly inclined with respect to the longitudinal axis of the tool, so that the pin and the guide slot cooperate to rotate the disc together with the feed wheels in one direction by one pitch as the forward end of the slide member is pressed against the workpiece. However, to utilize the engagement of the pin with the inclined guide slot at the initial operative stage of one working cycle invites such a disadvantage that a greater force is initially required for pressing the forward end portion of the tool against the workpiece, causing inefficiency in driving the screws into the workpiece. This disadvantage may be eliminated by decreasing the inclined angle of the guide slot. In this case, however, another disadvantage is invited that a stroke required for driving the screws becomes longer, causing undesirable increase in the entire longitudinal length and weight of the apparatus, which, in turn, causes difficulty in manipulation and inefficiency in operation.
Further, the prior art mechanism disclosed in the U.S. patent referred to in the foregoing has a further disadvantage caused by a fixed type nose piece. As is well known, it is necessary to provide a certain distance of space between a belt guide or retainer and the front end wall of the nose piece in order to make a selected self-drilling screw properly positioned within the space prior to driving the screw into the workpiece. As a matter of fact, however, various sizes of self-drilling screws are employed in industry. Therefore, if the above-mentioned space is shorter than the entire length of the screws to be driven, the nose piece must be replaced with a larger one. On the other hand, if the above-mentioned space is excessively larger than the entire length of the screws, working efficiency is diminished because of the uselessly longer stroke in each working cycle.
Still further, the prior art mechanism disclosed in the above-referred U.S. patent has a further disadvantage that a driver member is likely to come out of a chucking member because of frictions between the driver member and the magazine belt when the driver member returns to its starting position from its operative position where the bit portion of the driver member passes through the magazine belt. Once the driver member is disengaged from the chucking member, the apparatus must be, in many cases, disassembled for re-attaching the driver member into the chucking member, which is very inconvenient.
It is, therefore, an object of the invention to eliminate the above-discussed disadvantages in the conventional apparatus.
Another object of the invention is to provide an improved screw feed apparatus which permits decrease in size and weight of the apparatus as well as efficiency in operation by diminishing a forward stroke of a screwdriving tool in each working cycle.
A further object of the invention is to provide an improved screw feed apparatus in which a pair of feed sprocket wheels are rotated by one pitch not in the course of forward stroke but in the course of rearward stroke of the screwdriving tool.
A still further object of the invention is to provide an improved screw feed apparatus which incorporates a novel, positionally adjustable nose piece to be pressed against a workpiece.
A yet further object of the invention is to provide an improved screw feed apparatus which incorporates means for preventing undesirable disengagement of a driver member from a chuck of the screwdriving tool.
Other objects, features and advantages of the invention will become more fully apparent from the detailed description given hereinafter in connection with the accompanying drawings. It should be understood, however, that the detailed description and specific examples, which indicate preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.
According to the present invention, there is provided a screw feed apparatus for use with a power screwdriving tool which comprises an internally threaded adapter detachable by threads to an externally threaded shank portion of the power tool, an elongated driver member datachable at one end to a chuck formed with the shank portion, a casing relatively slidably mounted on the adapter, at least one spring disposed within the casing for urging the adapter axially outwardly, a pair of brackets mounted to a forward end of the casing and provided with guide means for guiding a flexible magazine belt in a direction transverse to a longitudinal axis of the power tool, the magazine belt carrying a series of self-drilling screws which are aligned in line and spaced at a regular pitch, a pair of feed sprocket wheels disposed within the brackets for feeding the magazine belt intermittently by the regular pitch, a nose piece mounted to a forward end of at least one of the brackets for providing a predetermined distance of screw receiving space between the forward end of the brackets and a workpiece into which the self-drilling screws are driven, a ratchet wheel supported by one of the brackets so as to co-rotate with the pair of feed sprocket wheels, a slide member supported on the casing so as to be axially slidable back and forth, the slide member being so arranged as to move toward the ratchet wheel in response to forward movement of the adapter and move away from the ratchet wheel in response to rearward movement of the adapter, and a claw means operatively supported by the slide member so as to force the ratchet wheel to rotate intermittently by the regular pitch as the slide member moves away from the ratchet wheel.
The apparatus according to the invention may preferably include means for adjusting relative positions of the nose piece to the mounting brackets and means for preventing the driver member from slipping out of the chuck.